Number of ballot sequences of length n having exactly one descent.

Terms

a(0) =1a(1) =5a(2) =16a(3) =43a(4) =99a(5) =215a(6) =430a(7) =834a(8) =1529a(9) =2765a(10) =4792a(11) =8216a(12) =13684a(13) =22575a(14) =36402a(15) =58285a(16) =91617a(17) =143097a(18) =220317a(19) =337100a(20) =509718a(21) =766655a(22) =1141457a(23) =1690994a(24) =2484138a(25) =3631902a(26) =5271297a(27) =7617750a(28) =10937657a(29) =15640771